The invention relates to optical networks, and more particularly relates to a system and method for per-band amplification of optical signals.
In optical networks, including dense wavelength division multiplexing (DWDM) optical networks, amplification of the optical signals is often required to traverse lengthy spans of fiber. Known methods of amplification utilize a single erbium doped fiber amplifier (EDFA) at, e.g., terminals, add/drop nodes and in-line amplifier nodes, with all DWDM channels sharing the same amplifiers as they pass through any one node. The EDFAs typically require more than one pump laser to achieve the output power required to support and amplify all of the channels or sub-bands passing through the node. The single EDFA solution also requires, in most instances, a gain flattening filter (GFF) to equalize the amount of gain for all of the channels across the usable bandwidth. The usable bandwidth is typically approximately 30 nm for a 40-channel system. These factors result in a relatively higher cost amplifier, and a relatively higher initial deployment cost, regardless of the number of channels initially deployed.
In certain optical network configurations, channels can be added/multiplexed relatively close to the ultimate destination point. These channels may require no optical amplification prior to arriving at the destination node. However, these channels share the same fiber with channels that have traveled significant distances over more lengthy spans of fiber, and hence require amplification. Both channels that do not require amplification as well channels that do require amplification, in present day network configurations, pass through at least one optical amplifier that amplifies all of the signals. This results in unnecessary amplification of those channels not requiring amplification, and a less efficient use of the available amplifier power.
There is a need for a more cost effective and more efficient optical amplification system for use in an optical network. The present invention is directed toward further solutions to address this existing need.
In accordance with one example embodiment of the invention, an optical amplification system includes an optical signal traveling through the optical amplification system. At least one amplifier is disposed to separately amplify each of the individual sub-bands.
At least one module of the optical amplification system is suitable for selectively separating or combining one or more individual sub-bands of the optical signal, in accordance with one embodiment of the invention.
A typical metropolitan optical network has a total of 160 wavelengths that are available for transmitting data. These wavelengths are divided into C and L bands, with 80 wavelengths in each band. Each C and L band is further divided into even and odd groupings, with 40 wavelengths in each group. Sub-bands, as referred to herein, comprise sub-groupings of the 40 wavelengths of each even and odd group, e.g., with three, four, or five wavelengths in each sub-band. The number of wavelengths in each sub-band, as understood by one of ordinary skill in the art, can vary depending at least partially on the application of the particular network. The examples illustrated herein utilize four wavelengths for each sub-band.
The module can be a bandpass filter, a channel add device, a channel drop device, a demultiplexer, a multiplexer, and/or the like.
The optical amplification system can be placed in an optical network where less than an entirety of optical sub-bands traveling through the network requires amplification. The optical amplification system, in such an instance, has disposed at least one amplifier to amplify each individual sub-band requiring amplification, and has disposed no amplifiers to amplify sub-bands not requiring amplification.
In accordance with another example embodiment of the invention, a method of optical sub-band amplification includes the step of providing an optical signal. The method also includes separating the optical signal into one or more sub-band, and then separately and individually amplifying the sub-band with one or more amplifiers.
According to further aspects of the invention, the separating step can occur by passing the optical signal through at least one bandpass filter, passing the optical signal through at least one demultiplexer, or passing the optical signal through at least one channel drop device.
In accordance with another example embodiment of the invention, a method of optical sub-band amplification, includes the step of providing an optical sub-band signal. The method continues by amplifying the optical sub-band signal with an amplifier. The optical sub-band signal is then combined with other sub-band signals, wherein one or more of the other sub-band signals has been separately and individually amplified by one or more amplifiers.
In such a method, the combining step can occur by passing the optical sub-band signal through at least one channel add device, or by passing the optical sub-band signal through at least one multiplexer.
In accordance with still another example embodiment of the invention, an optical amplification node is provided in an optical network. The optical network includes at least one optical signal propagating through the network. The optical amplification node includes at least one module, suitable for one of selectively separating and combining one or more individual sub-bands of the at least one signal. At least one amplifier is disposed to separately amplify the one or more individual sub-bands.
The optical amplifier node, in such an arrangement, includes at least one module in the form of a bandpass filter, a channel add device, a channel drop device, a multiplexer, and a demultiplexer.
In accordance with still another embodiment of the present invention, the optical amplifier node can be utilized as a per-band attenuator by not pumping the gain region.